Accelerating the solution and equilibrium of gases injected into a liquid, such as air, oxygen, ozone or chlorine in the treatment of liquids, for example water.
Infusion of gases into a flowing stream of liquid is commonplace in many industries. Perhaps the best-known example is treatment of water with ozone, oxygen, air, or other gases for purification purposes. There are many techniques to accomplish this, all of which involve presenting the gas to the liquid at a liquid/gas interface so the gas (or some of it) will dissolve in the liquid, passing across the interface.
There are several most frequently encountered techniques for creating the interface. One example is to spray the water into air so the surfaces of the liquid droplets form the interface. Another is to pour the liquid over extended surfaces such as Raschig rings to spread out the surface of the water to form an extended interface. Another is the injection of bubbles into a body of water. This technique can be accomplished simply by bubbling gas through the water, or as more pertinent to this invention by injecting the gas into a pressurized closed flowing stream of water with the use of an aspirating injector.
In the latter two techniquesxe2x80x94bubbling and injecting, the interface is the concave boundary of the gas bubbles, rather than the flat or convex exposed surface of the water. The transfer of the gas into the liquid requires its passage across the interface formed by the gas trapped in the bubbles. Although there are other pertinent parameters, those of most importance are the surface area of the bubbles and the system pressure.
It is well-known that a large number of smaller bubbles will have a larger total interface area than a single large bubble containing the same total volume of gas. It follows that the rate of transfer of a given volume of gas will be accelerated by reduction of the size of the bubbles, considering equal volumes of gas.
Also, the solubility of a gas in a liquid is a direct function of the pressure (Henry""s Law). More gas will be dissolved in a given liquid at a higher pressure (at the same temperature) than the same gas at a lower pressure.
Another parameter, which is more related to dynamics than to pressure and area at the interface is the partial pressure and the concentration of the gas intended to be transferred at the interface. For example, when air is injected the gas desired to be transferred is oxygen, rather than nitrogen and the other constituents of air. Their rates of transfer may not be equal, and it is possible that the concentration of oxygen at the interface may be lower than the concentration farther away from it. While the effect may be small for each bubble, in this invention many thousands of small bubbles are contemplated and even minor differences can provide major effects.
Because in some applications there may even be an exchange of gases from the water into the bubbles and vice versa, any means to accelerate the transfer is a welcome improvement. In conventional installations, it is common practice simply to employ enough volume of apparatus to provide time for the interchange to occur. This frequently necessitates the use of large tanks and towers, or large conduitry. These are expensive in themselves and require substantial xe2x80x9creal estatexe2x80x9d to accommodate them in major systems.
Instead of the above, or in addition to it, apparatus is known to stir or otherwise mix the gas and liquid. For example, static mixers are known which function to cause internal movement in the fluid stream with the objective of providing a uniform xe2x80x9cavailabilityxe2x80x9d of the gas bubbles and liquids, thereby to assure a uniformity of fluid in the system, avoiding voids and pockets, and local concentrations.
Such static mixers ordinarily redirect the stream or portions of it to change a smooth stream into a path with cross-currents, orbital currents, and the like. In some, downstream-directed stream converge into one another as they flow through the mixer. Their objective is to mix the components of the stream to approach uniformity and eliminate regions of greater or lesser concentration. They are as useful in blending syrups as in mixing liquids and gases.
However, that is not the objective of this invention. Instead, this invention is directed toward the vigorous and rapid continuing renewal of the interface conditions between the bubble and the surrounding liquid. The objectives are very different from those of the static mixer.
It is further useful to emphasize that the stream in this system, while closed and under pressure is not incompressible. In fact it is compressible, and in a sense elastic. This is because of its substantial gas content which often may be as high, volummetrically, as 20%. The liquid is, of course not compressible, but because of the gas, the combined stream is. Therefore changes in pressure, physical forces such as abrupt accelerations, impacts and reversals, result in important changes in the shape and size of the bubbles. The consequence is that the composition at the interface of the gas bubble with the liquid is being constantly renewed.
While neither the reactor nor the collider has any moving parts, it is not a static mixer in the conventional sense. The exercise of this stream is far from orderly. Its abrupt reversals, eddy regions and internal nozzles and joggles, all combine to cause this compressible stream to undergo physical reactions that profoundly accelerate the solution of the gas into the liquid.
The applicant has discovered that the rapid renewal of the interfaces and of the gas concentration directly contiguous to this interface has an extraordinary cumulative effect on the transfer of gases. He has also discovered that a most appropriate way to accomplish this is by the xe2x80x9cexercisingxe2x80x9d of the gas bubbles, for example by abrupt changes in direction of the stream, of passing the stream through sequential orifices, and of colliding streams of bubble-containing liquid. These techniques can be used singly or in any combination. Such exercise of the bubbles results in a surprisingly effective and very rapid solution and equilibrium of the gas.
This invention overcomes the disadvantages of the prior art by including in a flowing system under pressure, a collider or a reactor of surprisingly small bulk, or both, located downstream from an aspirator injector. For some applications this may advantageously be followed by an optional gas separator to remove undissolved excess gas.
This invention provides an optimum system which provides surprisingly beneficial results. However, there are many applications where ultimate performance is unnecessary. In this, an installation of lesser complexity and bulk can provide a myriad of small bubbles of gas to be dissolved and treated with sufficiently acceptable results.
The reader is entitled to ask why there is an advantage in accelerating a process which, if given enough time would occur anyway. The answer is that for a given volume of liquid and desired attained result it is possible to reduce the bulk and footprint of the system (and thereby its cost), and to reduce the dwell time of the liquid during treatment.
There is the additional advantage that the system need not be xe2x80x9cover-dosedxe2x80x9d in order to be certain that sufficient gas is available, and then requiring the stripping off a large excess quantity of treatment gas.
The rapid renewal and abrupt changes of the interfaces caused by the fluid manipulations of this invention result in a surprising reduction in dwell time and bulk of the process equipment. When the preferred embodiment of the system is utilized, the dwell time can often be reduced by as much as 60%, with an attendant reduction of required real estate and investment, compared to known systems.
The presently preferred embodiment of the invention receives liquid under pressure to be treated by an injected gas. The liquid flows into an aspirator injector which injects the gas into the liquid. From the injector, the flow is to a collider and a reactor, in either order, in which the stream is subjected to vigorous exercising including abrupt changes in motion rapidly to renew the gas/liquid interfaces.
From these (or from either one if only one is used) the stream is discharge, preferably through a centrifugal gas/liquid separator.
According to a preferred but optional feature of the invention, the collider provides for two colliding stream which create the vigorous action.
According to yet another preferred but optional feature of the invention, the reactor includes a cylinder having an upstream chamber and a downstream chamber with a partial barrier between them. An inlet nozzle directs a strong stream against a reflector surface on the barrier, which reverses the direction of flow in the chamber to a cove surface that again abruptly reflects the stream. The stream flows through joggle slots into the downstream chamber where it preferably strikes a cove surface that reflects the stream to a downstream facing reflecting surface, from which the stream resumes its flow toward the separator.
The above and other features of this invention will be fully understood from the following detailed description and the accompanying drawings, in which: